A crystal plasticity constitutive model for Ti3Al single crystal was established based on slip deformation mechanism within the frame of crystal plasticity theory, and it was compiled to a program to describe it by means of secondary development of ABAQUS/UMAT user subroutine. Then we applied it to simulate the mechanical behaviors of Ti3Al single crystal with different orientations during unidirectional compression deformation. The activation of slip systems and the interaction between activation and orientation has been analyzed. The simulation results show that basal slip of (0001)<112(—)0>, prismatic slip of {101(—)0}<112(—)0> , and pyramidal slip of {112(—)1}<112(—)6> can be activated. However, there are dramatic diference on the ease or complexity of activation of various slip systems, which is due to the difference of critical shearing stress and schmid factor. It is difficult for basal slip and pyramidal slip to be activated because of their larger critical shearing stress, which leads that the activation of basal slip and pyramidal slip just occurs with larger schmid factor. Pyramidal slip systems only can be initiated when compression axis is close to [0001] direction due to the maximum shearing critical shearing stress, especially. Prismatic slip is much easier to be activated and also has the largest contribution to plastic deformation. Furthermore, the simulation results were compared and in good agreement with the experimental results.